Currently, Puppet Strings only supports Puppet Tasks. Since Plans are
sort of connected to Tasks, it seemed right that Strings should also
support Plans. That and Plans are a thing that needs to be documented.
First, the Puppet[:tasks] setting needs to be set to add the 'plan' keyword to the Puppet Parser's lexicon, so this sets it in the Strings parser if the setting exists. If it does not exist and Puppet.version is less than 5.0.0, Strings will error out.
Second, processing for the Plans themselves is set up. Plans are very
similar to other Puppet objects like defined types and classes, so this
involved some serious copy-pasta.
Third, all the template/to_hash scaffolding for the different outputs is in place (HTML,
JSON, Markdown).
Yey.

Currently, puppet-strings does not know how to generate documentation
for Puppet Tasks. This does all the work to add support for Tasks
including a new JSON parser, a task handler, task statement, and task code
object. Basically, Strings reads the JSON using the native ruby json
parser and sends values through in a way it understands. It is only
passing json key/value pairs through, nothing is happening with tags at
this time. You can now document Tasks and generate HTML, Markdown, or
JSON output.

Previously, overload objects were not displaying their tags when
they had no docstring text. This was due to an issue in the overload
`to_hash` method, which prevented the tags from being serialized when
the dispatch had no top-level text. This commit updates that logic
so that the tags will always be included in the hash if they exist.

Previously, Strings ignored calls to `return_type` in Puppet 4.x API
function dispatches, preventing the return types of overloads from
being automatically determined. This commit adds a check for a node
with a `return_type` call and handles it properly.

Prior to this commit, strings did not properly handle providers
which had multiple related `defaultfor`s. In code, these are written
as comma-separated constraints. This commit updates strings' puppet
provider handler, as well as the template which generates HTML for
`defaultfor` statements.
Note that it was necessary to make a breaking change to the JSON
schema to accomodate multiple AND'ed defaults. Previously, provider
defaults were contained in a single key-value map. Now, they are
contained in an array of key-value lists, which allows multiple
constraints to be associated with each other.

The specs test functions written in the Puppet language in a few places, but
this feature is only supported in Puppet 4.1+. This commit prevents these
specs from running if targeting older versions of Puppet.